The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Sensitive and cost-effective DNA detection methods have a wide range of applications, from clinical diagnostics and drug development to the food industry and forensic sciences [Tang et al., Clin. Chem. 43(11): 2021-2038 (1997); Valasek et al., Adv Physiol Educ 29(3): 151-159 (2005); Mandal et al., Am. J. Food Technol 6: 87-102 (2011); van Oorschot et al., Investig genet 1(1), 14 (2010)]. In medical diagnostics, especially for infectious diseases, DNA detection technology such as quantitative polymerase chain reaction (qPCR), restriction fragment length polymorphism (RFLP) and ligation detection reaction (LDR) are crucial diagnostic tools [Landegren et al., Science 242(4876): 229-237 (1998); Kubista et al., Mol Aspects Med 27(2-3), 95-125 (2006); Handal et al., Expert Review of Molecular Diagnostics 6(1), 29-38 (2006)]. Fluorescence has been used almost exclusively as the DNA detection method in these tools due to its simplicity and high sensitivity [Kubista et al., Mol Aspects Med 27(2-3), 95-125 (2006); Handal et al., Expert Review of Molecular Diagnostics 6(1), 29-38 (2006)]. Recently, numerous efforts have been made to seek more cost-effective DNA detection technologies, notably for use in the developing world, yet none of them achieve the same sensitivity and applicability as fluorescence-based methods [Li et al., PLoS ONE 6(12): e29224 (2011); Diakite et al., Lab Chip 12(22): 4738-4747 (2012); Leslie et al., J. Am. Chem. Soc. 134(12): 5689-5696 (2012)].
Another approach to detect and quantify DNA in diagnostic reactions is to measure the solution viscosity [Livak-Dahl et al., Lab on a Chip 13(2): 297 (2013); Srivastava et al., Anal. Chem. 77(2): 383-392 (2005)]. The viscosity of a double-stranded DNA (dsDNA) solution at a known temperature depends on the mass concentration and the average length of the DNA strands. The solution viscosity can indicate DNA concentration and/or length [Huggins J. Am. Chem. Soc. 64(11): 2716-2718 (1942); Ross et al., Biopolymers 6(8): 1005-1018 (1968); Tsortos et al., Biopolymers 95(12), 824-832 (2011)]. In restriction digestion reactions the solution viscosity decreases as longer DNA strands are cut into shorter pieces. Alternatively, in PCR, the solution viscosity increases as the length of the DNA increases, through polymerization of the target sequence.